© 2004 Plant Management Network.
The Response of Fusarium graminearum-Infected Seed of Hard Red Spring Wheat to Vitavax Extra RTU and Dividend XL Seed Treatments
Jochum J. Wiersma, Assistant Professor, University of Minnesota, Department of Agronomy & Plant Genetics and Northwest Research and Outreach Center, 2900 University Avenue, Crookston 56716; and Herman J. Kandel, Extension Educator, University of Minnesota Extension Service, Coffey Hall, St. Paul 55108
Wiersma, J. J., and Kandel, H. J. 2004. The response of Fusarium graminearum infected seed of hard red spring wheat to Vitavax Extra RTU and Dividend XL seed treatments. Online. Plant Health Progress doi:10.1094/PHP-2004-0416-01-RS.
Fusarium head blight (FHB) caused by Fusarium graminearum can severely impact seed quality and limit the availability of seed. Repeated outbreaks of FHB in the hard red spring wheat (HRSW) production areas of Minnesota and North Dakota since 1993 has forced seed dealers and producers, on occasion, to use FHB-infected wheat as seed. In this experiment, two FHB-infected seed lots, one of the variety Verde and one of the variety 2375, were used to determine the effect of Vitavax Extra RTU (16.7% carboxin : 1.2% imazalil : 1.5% thiabendazole) and Dividend XL (16.5% difenoconazole : 1.38% mefenoxam) on initial plant population, grain yield, and quality. The standard laboratory germination tests indicated that germination of Vitavax Extra RTU-treated seed increased germination from 64 to 84% for both seed lots. Using a four-by-two factorial design, the effect of the brand of seed treatment, the effect of using either brand of seed treatment versus not using a seed treatment at all, and the attained germination percentages from the laboratory tests were used to determine the effects on the initial plant population, grain yield, test weight, and grain protein content. In three field trials, there was no significant interaction between the use of either Vitavax Extra RTU or Dividend XL and seeding rate for initial plant population, grain yield, and test weight. Although a treatment of FHB-infected wheat seed with Vitivax Extra RTU increased germination in a laboratory test, there was no increase in initial plant population or grain yield and quality compared to untreated seed. However, increasing the seeding rate in field trials compensated for poor germination results in the laboratory test and resulted in higher initial stands. Consequently, results of the laboratory test of the untreated seed needed to be used to calculate a proper seeding rate for both seed lots.
Fusarium head blight (FHB) or scab has impacted hard red spring wheat production in the north-central USA and Canada since the early 1990s (9). FHB is caused by Fusarium graminearum and the disease can severely impact yield and grain quality of wheat. The effects on grain quality are the characteristic tombstone kernels, which reduce test weight and thousand-kernel weight. In addition the vomitoxin deoxynivalenol (DON) may also be present (8).
If FHB-infected grain is to be used as a seed source, the recommendation is to thoroughly clean and condition seed to remove most of the FHB-infected kernels and improve test weight. A laboratory test to determine percent germination and seed vigor, as well as application of a fungicide seed treatment to improve stand and vigor, are recommended (10). The minimum standards are a test weight of 56 lb/bu and germination equal to or greater than 85% (6). The repeated outbreaks of FHB in the HRSW production areas of Minnesota and North Dakota since 1993 have forced seed dealers and producers to use FHB-infected wheat as seed in years when supplies of good quality seed were limited.
The germination of FHB-infected seed was improved substantially when the seed was treated with Vitavax Extra RTU (unpublished data). The objective of this research was to evaluate the effect of two common seed treatments on the initial plant population, grain yield, protein content, and test weight of two HRSW seed lots severely damaged by FHB.
To test the effect of Vitavax Extra RTU or Dividend XL on FHB-infected seed, two experiments were conducted. In the laboratory experiment, the percent germination of untreated seed and seed treated with Vitavax Extra RTU was determined. Using the percent germination obtained in these laboratory tests, a field experiment was conducted at two locations and two years in which the effects of Vitavax Extra RTU and Dividend XL on the initial plant population, grain yield, and grain quality were evaluated. Vitavax Extra RTU (Gustafson LLC, Plano, TX) is a formulation of 16.7% carboxin, 1.2% imazalil, and 1.5% thiabendazole. Dividend XL (Syngenta, Greensboro, NC) is a formulation of 16.5% difenoconazole and 1.38% mefenoxam. Both fungicides have a broad spectrum of activity and are labeled for use on wheat to control seedling blights caused by black point and FHB. The fungicide seed treatments were applied at the labeled rates of 5.0 fl oz/cwt and 1.0 fl oz/cwt for Vitavax Extra RTU and Dividend XL, respectively.
Laboratory Germination Test
Germination of seed lots Verde and 2375 were evaluated. The test weights of the seed lots were 59.8 and 61.2 lb/bu for Verde and 2375, respectively. The seed counts were 14500 and 13900 for Verde and 2375, respectively. Both seed lots had less than 4% visually scabby kernels (VSK) when using the scoring method described by Jones and Mirocha (8). Neither the test weight, kernel count, nor the percent VSK were cause for concern about the quality of the seed lots. Percent germination was determined by placing 25 seeds of each seed on a wet blotter towel and placing the folded blotter towel in a germination chamber at 68°F (1). The number of healthy seedlings was counted at 7 days. This test was repeated four times on each seed lot. Average germination was 68% for untreated seed of both seed lots. Germination of both seed lots treated with Vitavax Extra RTU averaged 84%.
Despite the low VSK score, both seed lots were damaged by FHB, as evidenced by seedlings in the germination test that were covered with pink mycelium, which is characteristic of F. graminearum (Figs. 1 and 2). This is in agreement with Gilbert and Tekauz (6) who have reported that, despite removal of lightweight and tombstone kernels, F. graminearum can readily be recovered from the seed when the crop was severely affected by FHB. F. graminearum can infect wheat anytime throughout kernel development (5). Infections at soft dough produce kernels with weights very similar to disease-free kernels or significant FHB symptoms (2). Therefore, depending on when the F. graminearum infections occurred during grain fill, seed lots with a low percentage of VSK may still have a much larger percentage of kernels that are infected with the fungus.
The Field Experiment
To test the effect of the seed treatments on both seed lots, a four-by-two factorial design with variety, seed treatment, and seeding rate (based on percent germination previously determined) as factors was planted in a randomized complete block with four replications at each location. The plot size was 5 by 25 feet. For each variety, the seeding rate was calculated based on the percent germination of the untreated seed (68%) as well as the treated seed (84%) using the following formula:
For the desired stand, a plant population of 1,250,000 plants per acre or 28.7 plants per ft2 was used. To calculate a seeding rate it was assumed that the expected stand loss equaled 15%.
In 1998, the experiment was planted on May 21 in Oklee, MN on a Ulen fine sandy loam (sandy, mixed, frigid Aeric Calciaquolls) and harvested on August 27. A second site was established at the Northwest Research and Outreach Center in Crookston, MN on May 17 (Hegne Fargo clay; fine, smectitic, frigid typic Epiaquerts and fine, smectitic, frigid typic Calciaquets) but was lost due to flooding later that summer. In 1999, the experiment was planted in Oklee on April 27 on an Ulen fine sandy loam. That same year, the experiment was planted on May 5 in Crookston on a Hegne Fargo clay (fine, smectitic, frigid typic Epiaquerts and fine, smectitic, frigid typic Calciaquets). Harvest was completed on August 11 and 15 in Crookston and Oklee, respectively.
Data collected included the initial plant population of wheat at the 2- to 3-leaf stage. To estimate grain yield, the entire plot was harvested with a small plot combine. Harvested grain was cleaned with a Clipper Office Tester and Cleaner (Seedburo Equipment Co., Chicago, IL) and grain yield and test weight were expressed on 13.5% moisture basis as bushels per acre and pounds per bushel, respectively. Grain protein content was determined on a 1 lb subsample by near infrared transmission using a Tecator Infratec 1229 Grain Analyzer (Foss North America, Inc., Eden Prairie, MN). The data were analyzed using Statistix 8 (Analytical Software, Tallahassee, FL) assuming all effects as fixed.
No significant interaction between the treatments and the environments was detected (data not shown), so data were combined across the three remaining locations. Initial plant population, grain yield, and test weight did not differ between seed that was treated with a fungicide or not (Table 1). These results are similar to those reported by Diehl et al. (4) who found that, even though seed treatments suppressed common root rot caused by Cochliobolus sativus in laboratory tests, it did not increase seed germination under field conditions.
Table 1 Initial plant population, grain yield, test weight, and grain protein content for seed treated with either Vitavax Extra RTU or Dividend XL versus untreated seed compared across varieties.
a Data is combined across 12 replications and three locations (Oklee in 1998 and 1999, and Crookston in 1999).
Initial plant population was significantly higher when the seeding rate was adjusted according to untreated seed germination (Table 2). However, this difference in initial plant population did not result in a difference in grain yield, test weight, or grain protein content (Table 2). No interaction could be detected between the factors of seed treatment and seeding rate for the initial plant population, grain yield, test weight, or grain protein content. There were no differences between Vitavax Extra RTU and Dividend XL for initial stand or any of the yield and grain quality parameters measured. Across treatments, variety 2375 yielded an average of 50.4 bu/acre, which was significantly less than Verde at 53.8 bu/acre.
Table 2 Initial plant population, grain yield, test weight, and grain protein content for two seeding rates compared across two varieties of HRSW that were treated with Vitavax Extra RTU and Dividend XL seed treatments.
a Data is combined across 12 replications and three locations (Oklee in 1998 and 1999, and Crookston in 1999)
b Seeding rate calculated based on the results of the laboratory germination test of seed treated with Vitavax Extra RTU.
c Seeding rate calculated based on the results of the laboratory germination test of untreated seed.
Based on the results of these trials, an application of either Vitavax Extra RTU or Dividend XL to FHB-infected seed of HRSW increased germination in laboratory tests but did not improve initial plant population, grain yield, or quality in the field compared to untreated seed. This is in contrast to results previously reported by Gilbert and Tekauz (6) as well as Jones (7). Gilbert and Tekauz (6) reported that a number of common fungicide treatments tended to improve germination and emergence of F. graminearum-infected seed. Jones (7) reported that thiabendazole -- one of the active ingredients in Vitavax Extra -- was the most effective to control seed-borne F. graminearum. Jones (7) also reported that difenoconazole -- one of the active ingredients in Dividend XL -- gave intermediate control of seedling blight caused by F. graminearum. Both Gilbert and Tekauz (6) and Jones (7) reported that seed treatments were more beneficial when soil temperatures were warmer. This is due to the fact that F. graminearum is more active in warmer versus cooler soils (3). This also may explaination why no differences could be detected in this experiment between seed treated with a fungicide and untreated seed. Especially in 1999, conditions following planting were cool (data not shown).
In addition it has to be noted that both seed lots tested in this experiment showed very few visible signs of infections with F. graminearum as evidenced by the low VSK score. F. graminearum can infect throughout the kernel development and cause seed-borne root rot when infected kernels are used for seed (2,5). In addition the seed may have been contaminated with viable spores of F. graminearum (7). These non-symptomatic, seed-borne infections of F. graminearum and/or F. graminearum contaminated seed caused the pink mycelium growth in the laboratory germination test of the untreated seed. The Vitavax Extra RTU controlled the F. graminearum in the laboratory germination test. Isolation of F. graminearium from seedlings of plots that were treated with a fungicide as well as untreated plots would have aided in the interpretation of the results. Unfortunately, no attempt was made to isolate F. graminearum or any other fungus from the seedlings in the laboratory test or in the field trial. Therefore, it is possible that both residue as well as other seed-borne diseases may have contributed to the observed results in the field trial.
Increasing the seeding rate in field trials compensated for poor germination in the laboratory test and resulted in a higher initial plant population. Consequently, results of the laboratory test of the untreated seed needed to be used to calculate an adjusted seeding rate. Using the higher seeding rate resulted in an initial plant population of 28.3 plants per ft2 which is less than 1.4% from the goal of 28.7 plants per ft2. Planting at a higher seeding rate to compensate for low germination in the laboratory germination test, however, did not translate to higher yields. The ability of spring wheat to tiller and thus compensate for a lower plant population may explain those results. In years when the growing conditions do not favor the development of tillers, larger yield differences may be expected.
We wish to thank Ray and Keith Swenson of Swenson Seed Farms for providing us with the seed and the experiment location in Oklee, and the Red Lake County Crop Improvement Association for their support.
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